The present invention is related to wireless networks, and in particular to a method and apparatus for carrying out a radio site survey.
Wireless networks such as wireless local area networks are becoming ubiquitous. For example, WLANs that conform to the IEEE 802.11 standard are found everywhere. Deployment of WLANs includes selection of locations to place access points (APs), frequency assignment, and determining of transmit powers. Properly solving this is called “radio planning.” Radio planning requires site surveys to determine the propagation properties of the environment. By a site survey is meant knowledge of path loss data, including path loss data from AP-to-AP, from AP-to-client, and from client-to-client for APs and clients whose location is known. By path loss data is meant actual path loss, or similar data, e.g., data from which the path loss can be determined. This similar data includes, for example, the received signal strength for a signal whose transmit power is known.
In addition to radio planning, path loss data also provides a mechanism for determining the location of wireless stations, e.g., the location of rogue access points.
Although AP-to-AP path losses can be obtained automatically, the other forms of path losses usually require inaccurate prediction software, or expensive human intervention, e.g., in a site survey/walkabout.
Path loss prediction software is available, for example, from Wireless Valley Communications, Inc. (Austin, Tex.), and others. See, for example, ProMan—Prediction of Wavepropagation (Path Loss & Wideband Parameters) by AWE Communications, Gärtringen, Germany. See also Constantino Perez-Vega, Jose Luis García G and José Miguel López Higuera, “A simple and efficient model for indoor path-loss prediction,” Meas. Sci. Technol. vol. 8, pp. 1166-1173, 1997. G. Wölfle, R. Wahl, P. Wertz, P. Wildbolz, F. Landstorfer “Dominant Path Prediction Model for Indoor Scenarios, German Microwave Conference (GeMIC) 2005, Ulm (Germany), April 2005. R. Hoppe, P. Wertz, F. M. Landstorfer, and G. Wölfle: “Advanced Ray Optical Wave Propagation Modelling for Urban and Indoor Scenarios Including Wideband Properties,” European Transactions on Telecommunications (ETT), January/February 2003 (Number 01/2003), January 2003. See also Hills, A.; Schlegel, J.; Jenkins, B.: “Estimating signal strengths in the design of an indoor wireless network,” IEEE Transactions on Wireless Communications, Volume 3, Issue 1, January 2004 Page(s): 17-19. See also U.S. Pat. No. 6,680,924 titled “Method for estimating signal strengths.”
It is known, however, that prediction software can produce significant errors. The accuracy of the predictions depends on the accuracy of the path loss model used, and on the knowledge of the architecture in which data is to be predicted. Actual measurements clearly are more accurate.
To perform a radio site survey typically involves obtaining actual walkabout data by having a person walking about the area of interest. Such a person may or may not have accurate location information. An example of how walkabout data without explicit knowledge of location is used in Cisco's Wireless LAN Solution Engine (WLSE), by Cisco Systems, Inc., related to the assignee of the present invention.
A radio site survey may also be obtained using fake walkabout data obtained from extrapolating AP-to-AP data, as per Cisco's Wireless LAN Solution Engine (WLSE), by Cisco Systems, Inc., related to the assignee of the present invention. See also U.S. Pat. No. 6,680,924 to Hills et al., titled METHOD FOR ESTIMATING SIGNAL STRENGTHS.
U.S. Pat. No. 6,581,000 to Hills et al., titled POSITION LOCATION SYSTEM AND METHOD describes a system for determining a position of a user, e.g., a person carrying a laptop that includes a wireless transceiver for obtaining walkabout data. The system includes a distance sensor in communication with a position-tracking device. The distance sensor is for detecting movement by the user, and the position-tracking device is for determining the position of the user based on detection of movement by the user and a relative change in direction input from the user. This system provides for a walkabout that includes position determining.
Hills, A. and J. Schlegel, “Rollabout: A Wireless Design Tool,” IEEE Communications, vol. 42, no. 2, pp. 132-138, February 2004, describes a semi-automated design tool called “Rollabout” that partially automates the collection and interpretation of site survey data. A rolling cart that contains a radio transceiver is pushed around an indoor area where a site survey is desired. When pushed around on the rolling cart, the system collects data from APs and automatically creates a coverage map of the region. Using this data, the described system also helps define optimal AP placement and determine the best frequency assignments for APs.
While Rollabout does go part of the way towards automating the obtaining of a site survey, Rollabout still requires a human to walk about the area. Furthermore, as described in the above-mentioned Hills et al. IEEE paper, Rollabout only measures AP-client path losses, not client-client. If it is also desired to measure client to client measurements, manually walking around involves a very large number of measurements. For example, if the number of AP-to-client measurements grows as O(N) with area, then the number of client-to-client measurements initially grows as O(N2) with area, which strongly motivates a fully automatic method that does not require a human to walk-about.
Thus there is a need in the art for an automatic mechanism for obtaining AP-to-client and client-to-client path losses. By automatic is meant a method that does not require a human to walk about and obtain the measurements.